These Orders may be briefly defined as follows,—the reader being asked to recall the fact that by a mandibulate mouth we understand one in which the mandibles, or the maxillæ, or both, are fitted for biting, crushing, or grasping food; while the term suctorial implies that some of the mouth parts are of a tubular form or are protrusible as a proboscis, which assists, or protects, a more minute and delicate sucking apparatus:— 1. _Aptera_ (ἀ without, πτερόν a wing). Wingless[108] Insects; mouth mandibulate or very imperfectly suctorial. Metamorphosis very little. 2. _Orthoptera_ (ὀρθός straight, πτερόν a wing). Four wings are present, the front pair being coriaceous (leather-like), usually smaller than the other pair, which are of more delicate texture, and contract in repose after the manner of a fan. Mouth mandibulate. Metamorphosis slight. 3. _Neuroptera_ (νεῦρον nerve, πτερόν a wing). Four wings of membranous {173}consistency, frequently with much network; the front pair not much, if at all, harder than the other pair, the latter with but little or no fanlike action in closing. Mouth mandibulate. Metamorphosis variable, but rarely slight. 4. _Hymenoptera_ (ὑμήν membrane, πτερόν a wing). Four wings of membranous consistency; the front pair larger than the hind, which are always small and do not fold up in repose. Mouth mandibulate, sometimes provided also with a tubular proboscis. Metamorphosis very great. 5. _Coleoptera_ (κολεός sheath, πτερόν a wing). Four wings; the upper pair shell-like in consistency, and forming cases which meet together over the back in an accurate line of union, so as to entirely lose a winglike appearance, and to conceal the delicate membranous hind pair. Mouth mandibulate. Metamorphosis great. 6. _Lepidoptera_ (λεπίς scale, πτερόν a wing). Four large wings covered with scales. Mouth suctorial. Metamorphosis great. 7. _Diptera_ (δίς double, πτερόν a wing). Two membranous wings. Mouth suctorial, but varying greatly. Metamorphosis very great. 8. _Thysanoptera_ (θύσανος fringe, πτερόν a wing). Four very narrow fringed wings. Mouth imperfectly suctorial. Metamorphosis slight. 9. _Hemiptera_ (ἡμι half, πτερόν a wing). Four wings; the front pair either leather-like with more membranous apex, or entirely parchment-like or membranous. Mouth perfectly suctorial. Metamorphosis usually slight. We must again ask the reader to bear in mind that numerous exceptions exist to these characters in most of the great Orders; for instance, wingless forms are not by any means rare in several of the Orders. Before remarking further on this system we will briefly sketch two other arrangements of the Orders of Insects, for which we are indebted to Packard and Brauer. PACKARD'S CLASSIFICATION.